Jikkai Sho 63-92859 published by the Japanese Patent Office in 1988 discloses a toroidal continuously variable transmission for a vehicle.
In this transmission, a speed ratio is varied according to a variation of a gyration angle of plural power rollers gripped between an input disc and output disc. The gyration angle of each power roller changes according to the displacement of a trunnion supporting each power roller. The trunnion displaces along a trunnion axis forming a right angle with the rotation axis of the input disc and output disc. Due to this movement, the input and output discs cause the trunnion a rotational displacement within predetermined limits centered on the trunnion axis, thereby varying the gyration angle of the power roller.
The axial displacement of the trunnion is achieved by applying a hydraulic pressure to a fixed piston via a shaft.
The displacement of the trunnion in the axial direction and its rotational displacement are fed back to a speed ratio control valve which controls the aforesaid hydraulic pressure by a precess cam attached to the end of the shaft. In this way, the oil pressure is controlled so that the continuously variable transmission reaches a desired speed ratio.